The discovery of the first human retrovirus proceeded rather independently in Japan and the United States. In 1980, Poiesz et al. (83) identified human T-cell leukemia virus (HTLV) in a T-cell line from a patient with cutaneous T-cell lymphoma. Independently, in 1982, Yoshida et al. (103) identified adult T-cell leukemia virus (ATLV). Soon, HTLV and ATLV were shown to be identical at the sequence level and were named HTLV type 1 (HTLV-1) (27).